In traditional wind turbines, the blades, i.e. often three blades in total, are attached to a hub which forms one of the two free ends of the drive shaft from which the converted energy is released, for example, by rotation of an electrical generator.
Bearings arranged between the hub and blades facilitate rotation and thus control of the blade angle relative to the hub. This allows control of the conversion ratio between the wind energy and the energy of the rotating drive shaft. The blades may, for example, be pitched completely out of the wind so that no conversion takes place, e.g., if the wind turbine is stopped for maintenance or due to strong winds.
In general, bearings for the blades are difficult to access and typically, proper maintenance and lubrication is important for the reliability of the wind turbine.
Means for improving the lubrication of bearings are known in various bearings. GB 2055154 discloses a container which can be contracted in response to increasing temperatures whereby grease is injected into a cavity via lubrication channels.
EP 1273814 discloses a bearing for a wind turbine where different lubrication channels are connected to containers for transporting grease away from a cavity of the bearing. In practice, it has been found difficult to handle such containers in the very narrow space in the hub of a wind turbine, and in particular, it has been found difficult and time consuming to replace containers which are filled up with grease.